A system and method for controllably releasing radiation in percutaneous radiation treatment is provided. In a preferred embodiment, a laser is coupled to an optical fiber that is inserted below the skin or into a vascular lumen to a predetermined point. The fiber is connected to a source of electromagnetic radiation such as a laser, non-coherent radiation source, high power laser diode, LED, and an ultrasonic source. Radiation is then delivered to the treatment site while the fiber is simultaneously drawn out to the entry point. The fiber is manually withdrawn and during this time the radiation is administered in a manner appropriate for the vein being treating in regards to power or energy level. To maintain a constant proper energy density, the speed of withdrawal is measured and sent to a controlling mechanism. The controlling mechanism modifies the power emitted, pulse length or pulse rate to ensure that the vein or tissue receives a consistent dose of energy during manual withdrawal. In one preferred embodiment, an imaging device provides the controlling device with position and time information so that speed information from fiber or catheter surface textural properties or based on one or more bar code like markings. In another preferred embodiment, additional information is collected, such as vein diameter prior to treatment, position of the distal end of the fiber, and/or impact measurements such as vibration or temperature during treatment, and the controlling mechanism adjusts output power or pulse rate in response to measurements to maintain a desired power density at all position during the manual withdrawal.